How does a man suddenly abandon his family in favour of an isolated life in a monastery? What is the legacy of Léonard's father's sudden departure? Mon père, le roi captures the painful memories of the son and ex-wife of a man turned “king” of a religious cult. Together with the filmmaker, they take to the road to visit the man who abandoned them 45 years ago. For Léonard, it is also a return to the prison where he spent part of his childhood, after having been abducted by his father.